Add hhvm support

[imsamurai]

• hhvm support
• chnage and simplify travis config

[wa0x6e]

Sorry for the delay.

I guess that the code changes has nothing to do with hhvm, and you just added hhvm to travis to prove that the current code works on it.

Storing all used keys in another key is a good idea, but there's always the danger that that key get pruned, and we lose all tracks of the used keys.

[coveralls]

Changes Unknown when pulling 4e81480 on imsamurai:master into * on kamisama:master*.

[coveralls]

Changes Unknown when pulling 4e81480 on imsamurai:master into ** on kamisama:master**.

[wa0x6e]

There's a lot of unrelated changes in this PR.

I suggest that you first make a PR with all the code standard fixes, then make another separate PR for the HHMV support.

[wa0x6e]

Docblock indentation and using tab for indentation should be left as is, as it's the standard used for Cake 2.x. The standard have changed in 3.x, but this plugin is for Cake 2.x, the 3.x version have memcached included by default.